1. Field of the Invention
The present invention relates to a pattern extracting apparatus which extracts a specific area such as a character section or a pattern section from a multicolored image in which, for instance, a character section and a pattern section are mixed.
2. Related Art of the Invention
A method to extract only a character section as a specific area out of a multicolored image in which the character section and the pattern section are mixed has been disclosed in the Japanese Laid-Open Patent Publicaition No. 03-191482. In this disclosed method, an image is divided according to the R (Red), G (Green) and B (Blue) color space and a required area only is extracted.
On the other hand, it has been also attempted to get color information according to a coordinate system which is close to human perceptive characteristic instead of RGB color space. One of the color spaces which are approximate to this human perceptive characteristic is the L*a*b* color space which has been specified by the CIE (International Commission on Illumination) furthermore a conversion expression has been made.
In addition, the handling of color information close to color names characterized by human color perception has been disclosed in the Japanese Laid-Open Patent Publication No. 02-67689. In this disclosure, it has been proposed to divide an image by grouping proper ranges after converting three primary color values into a color space approximate to human perceptive characteristic.
When extracting a specific area from a color image, the image was divided according to (1) three primary color values, (2) a color space approximate to human perceptive characteristic converted from the three primary color values or (3) a set expressed by color names based on the approximated color space. However, this method has such problems as described below.
(1) The three primary color space of RGB is a distorted space which is not uniform when viewed from human perceptive characteristic. Therefore, no sufficient accuracy is obtained when a color image is divided according to this coordinate system.
(2) The problem in (1), above can be improved in case of a space approximated to human perceptive characteristic from three primary color values, for instance, the L*a*b* color space. However, when compared with the Munsell color system which experimentally represented human perceptive characteristic, its error is large.
(3) As described above, the approximating accuracy of this color space is not sufficient. Therefore, the result of division of a color image corresponding to human senses cannot be obtained from classification of color names based on the approximated color space.
Thus, a specific area cannot be precisely extracted from a multicolored image precisely.